1. Field of the Invention
The present invention relates generally to devices having particular utility in the diagnosis and treatment of conditions of the eye. In particular, the invention relates to devices useful as ophthalmologic occluders to assist in the diagnosis of various conditions of the eye, such as stabismus, heterophorias, cyclophorias and the like.
2. Description of the Related Art
Conditions of the eye involving muscular imbalances or misalignments, such as manifest deviations (heterotropias) or latent deviations (heterophorias), are fairly common disorders which can be treated through the use of appropriate corrective devices or therapeutic maneuvers. Unfortunately, the existence of the condition may not be readily apparent to the afflicted individual, such as where the condition is latent or in early stages of progression. Identification and correction of such problems are made even more difficult by the fact that their diagnosis typically involves a fair degree of subjective physician skill as well as familiarity with the signs of the condition, signs which are often difficult to discern or recognize.
Latent strabismus, or heterophoria, is a condition involving a latent misalignment of the eyes. One test commonly employed by physicians to identify latent strabismus is the so-called "cover test". In the cover test, one of a patient's eyes is covered or "occluded" and the patient is asked to look at or "fix" on a particular point using his other eye. When the cover or occluder is removed, the misaligned eye often makes a readjustment movement that is distinctive of the particular defect; e.g., a "fusional" movement in the case of heterophoria, or a "refixation" movement in the case of a manifest deviation. To induce the refixation movement, the occluder often needs to be repositioned to cover the fellow eye.
Unfortunately, when conventional occluders are used the cover test method requires a fairly high degree of experience and ability from the observer, in that the readjustment eye movements are often quick and difficult to discern. The difficulty is compounded by the fact that the occluder itself tends to obscure the observers ability to see certain eye movements. For example, if a latent strabismus exists, the occluded eye moves in a distinctive fashion but these movements are obscured by the occluder and thus go unnoticed by the observer.
Moreover, certain alignment deviations can't be diagnosed readily through the use of the conventional cover test. For example, in the case of cyclophoria, a latent rotational stabismus in which the eye moves around an anterior/posterior axis, the eye movement is of a very small amplitude. Where a conventional occluder is employed, these small movements are not generally discernable. For this reason, the diagnosis of cyclophoria has generally required complex instrumentation, subjective diagnostic techniques or both.
One type of occluder which has been designed in an attempt to address these problems is the so-called frosted glass occluder. As the name implies, the frosted glass occluder employs partially opaqued frosted glass in place of an entirely opaque occluding surface. However, the frosted glass occluder has not met with much success. This is because although the frosted glass appears to do a fairly good job as a conventional occluder, it suffers from many of the same drawbacks as the conventional occluder--the frosted glass tends to obscure the observers view to a significant extent, making the instrument virtually useless for detecting conditions where a transparent rather then translucent view of the eye is needed to detect fine eye movements.
Various other methods and devices are known which are used as an aid in the diagnosis of latent or manifest strabismus. One such device, the "Maddox Rod", is a instrument used to estimate or measure the type or the amount of an ocular misalignment based on the information given by the patient. It is an instrument that measures the subjective deviation. Other devices such as the synoptophore, can be used to determine the type and amount of an occluder misalignment both in subjective and in objective ways. Unfortunately, these devices and methods are either highly subjective in nature or involve complex and expensive instruments. In any event, none of these instruments allow direct detailed observation of the eye through the occluder while the eye is in an occluded state.
The problems enumerated in the foregoing are not intended to be exhaustive but rather are among many which tend to impair the effectiveness of previously known methods and devices for testing for misalignment of the eyes. Other noteworthy problems may also exist; however, those presented above should be sufficient to demonstrate that the prior devices and techniques appearing in the art have not been altogether satisfactory.